Humanists UK also offer your school a free copy of 'What is Humanism?
How do you live a good life without a god? And other Big Questions for
Kids' by Michael Rosen and Annemarie Young, it gives young people
an excellent introduction to Humanism. It can be requested here

Keeping children
safe in education: Statutory guidance for schools and colleges (July
2015)
54. In a school or college, a supervised volunteer who regularly teaches
or looks after children is not in regulated activity. The Department
for Education (DfE) has published separate statutory guidance on supervision
and regulated activity which schools and colleges should have regard
to when considering which checks should be undertaken on volunteers.
Non-regulated activity does not require a DBS check